The identification of ARF, a component of the adenylate cyclase system, as a GTP-binding regulatory protein is of considerable interest due to the similarities between ARF and the products of the ras oncogene (molecular mass, membrane location, GTP binding characteristics). In addition, expression of ras proteins has profound effects on cyclic nucleotide levels in some systems. ARF was purified from bovine brain membranes. Cyanogen bromide fragments of the pure protein were separated and two amino acid sequences of about 25 residues each were obtained. Synthetic peptides were synthesized for injection into rabbits to produce specific antibodies to ARF. Oligonucleotide probes were also synthesized from the amino acid sequence and are being used to screen a cDNA library to obtain the full length sequence of ARF. These antibody and cDNA probes should help to identify the site and physiological role of this novel membrane protein. Comparison of the primary and predicted tertiary structure of ARF to other recently cloned G-proteins may aid in the identification of specific domains involved in binding other proteins or binding and hydrolyzing GTP. In this case, site-directed mutagenesis will be used to construct specific altered proteins to test for cellular functions of ARF.
